Semi-pelagic Longline and Trammel Net Elasmobranch Catches in Southern Portugal: Catch Composition, Catch Rates and Discards

Abstract

In Portugal, elasmobranch landings have decreased substantially in recent years. In this work, elasmobranch catches in experimental hake near bottom semi pelagic longlines (1997 and 1998) were compared with those of experimental trammel nets (2000). In the hake semi pelagic longline fishery, 7 elasmobranch species represented 33.4% (2185 specimens) of the total fish captures. The most abundant species were Galeus melastomus (63.3%), Etmopterus pusillus (21.7%) and Scyliorhinus canicula (14.2%). Most of these elasmobranchs (68.3% in total) were discarded. In the trammel net fishery, 16 different elasmobranch species represented 4.3% (597 specimens) of total fish catches and the most important species were Raja undulata (43.6%) and Scyliorhinus canicula (10.2%). The majority of the elasmobranchs caught with this gear had commercial value, and only 5.4% were discarded. In both fisheries, intra -specific catch rates varied with depth. Length frequency distributions for the only species with relatively high catches in both fisheries, the small-spotted catshark, showed that in general, trammel nets catch larger specimens and in a more restricted length range than longlines. Introduction Elasmobranch fishes have life strategies that make them especially vulnerable to overexploitation (Pratt and Casey, 1990; Smale and Goosen, 1999; Wintner and Cliff, 1999; Hazin et al., 2002; Coelho and Erzini, in press). Worldwide, the problem of elasmobranch overexploitation has been well documented for the case of targeted fisheries (Bonfil et al., 1990; Campbell et al., 1992; Hurley, 1998; Stevens at al., 2000) as well as those with high levels of by-catch of these species (Buencuerpo et al., 1998; Mckinnell and Seki, 1998) and for other fishing activities, such as recreational fishing (Francis, 1998). Elasmobranch fishes are a very important component of the by-catch of the artisanal fisheries in Portugal (Erzini et al., 2000; Erzini et al., 2001), but no management program has been established yet. In the past few years, catches decreased 46.3% in the Algarve (from 888.1 t in 1988 to 447.0 t in 2000) and 30.1 % at a national level (from 5634.4 t in 1997 to 3938.6 t in 2000) (DGPA, 2000). In some cases, those reductions have been very drastic and might even indicate that these species are at high risk. Such is the case of the gulper shark (Centrophorus granulosus) where there was a catch reduction of 92.3 % at a national level and 80.4 % in the Algarve, or the smooth hounds (Mustelus spp.) that registered reductions of 79.4% at a national level and 54.2% in the Algarve. The rays and skates (Raja spp.) have also suffered great reductions, namely 43.8 % at a national level 48.7 % in the Algarve.